The deliberately unwieldy full title of US playwright Jackie Sibblies Drury’s work is (deep breath) We Are Proud To Present A Presentation About The Herero Of Namibia, Formerly Known As Southwest Africa, From The German Sudewestafrika, Between The Years 1884-1915. But the drama lurking behind it is a genuine short, sharp shock.

A group of unnamed actors gather before us to rehearse their drama school-style project: a play about the first genocide of the 20th century, the colonial German-orchestrated attempt to exterminate the Herero and Nama people. Their source material is a cache of letters written by German soldiers to their sweethearts back home.

Actorly concerns (‘I don’t know what my active verb is’) and some mildly abrasive exchanges ensue but, soon, the inadequacy of these documents – which offer no African perspective on this horrific episode of history – start to cause serious anger in the ranks of the half-black, half-white cast.

Light-hearted moments of improv beatboxing and adopting silly accents and stereotypes morph into dagger-sharp outbursts about black representation, lost heritages, slanted histories and who has the right to portray different peoples’ experiences.

As the increasingly personal attacks mount up, director Gbolahan Obisesan’s production adopts the same trajectory as the best horror films, building events to an inexorable, awful climax.

Drury’s excoriating drama really is theatre in the raw, which by the end takes your breath away with its vicious dissection of the gulf in understanding between black and white, gradually scything through social niceties to expose a putrid core.

It’s all the more effective here thanks to Obisesan’s handling of its lulling spiky humour and undaunted performances from all the cast.

Ayesha Antoine’s Actor 6, nominally in charge but increasingly unable to control what’s happening, and Kingsley Ben-Adir’s furiously dissenting Actor 2 stand out – but it’s the mute final anguish of Isaac Ssebandeke’s Actor 4 that leaves you with a lump in your throat.